4 years ago

Integration of Bromine and Cyanogen Bromide Generators for the Continuous-Flow Synthesis of Cyclic Guanidines

Integration of Bromine and Cyanogen Bromide Generators for the Continuous-Flow Synthesis of Cyclic Guanidines
Gabriel Glotz, C. Oliver Kappe, Doris Dallinger, René Lebl
A continuous-flow process for the in situ on-demand generation of cyanogen bromide (BrCN) from bromine and potassium cyanide that makes use of membrane-separation technology is described. In order to circumvent the handling, storage, and transportation of elemental bromine, a continuous bromine generator using bromate–bromide synproportionation can optionally be attached upstream. Monitoring and quantification of BrCN generation was enabled through the implementation of in-line FTIR technology. With the Br2 and BrCN generators connected in series, 0.2 mmol BrCN per minute was produced, which corresponds to a 0.8 m solution of BrCN in dichloromethane. The modular Br2/BrCN generator was employed for the synthesis of a diverse set of biologically relevant five- and six-membered cyclic amidines and guanidines. The set-up can either be operated in a fully integrated continuous format or, where reactive crystallization is beneficial, in semi-batch mode. Cyanogen bromide on tap: The highly toxic but synthetically powerful reagent cyanogen bromide (BrCN) was generated in a fully continuous fashion from benign precursors and directly used for the synthesis of medicinally relevant N-heterocycles.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201708533

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